Fluid valves exist in a wide variety of forms and sizes, serving a multitude of purposes, handling flowable materials whose characters range from light gaseous to heavy slurries and near-solids, and operable at various speeds under controls as diverse as simple binary (ON-OFF), proportional, direct-manual and remote-electrical. Those which are capable of responding quickly to govern even relatively large flows with precision, and with expenditure of little electrical power, are of special interest in certain industrial processing, such as the automatic regulation of gases in semiconductor and integrated-circuit manufacturing. Mass flow controllers, for example, are widely used in semiconductor and integrated-circuit manufacturing to control the delivery of process gases, and the mass flow controllers include such valves.
U.S. Pat. Nos. 4,796,854, 5,727,769, and 6,505,812, which are all assigned to the assignee of the present disclosure, show examples of solenoid proportioning valve assemblies. The disclosed valve assemblies all include movable valve members positioned by an armature to open and close a valve orifice.
The valve assemblies may use metals seals or elastomeric seals. The use of metal sealing, or seating, surfaces eliminates permeation from the atmosphere and the outgassing and particle generation inherent to elastomeric seals. Other materials, such as glass, sapphire, or ceramic, may be used as the seating surfaces to avoid chemical degradation from the particular fluid being controlled by the valve assembly, and/or degradation due to temperatures and pressures, for example.
It is often preferable to use sapphire in place of metal in the seating surfaces of valve assemblies. In high accuracy valve assemblies used for the precise delivery of gases, metal seating surfaces may require a hand-lapping final operation to customize orifice surfaces to provide suitable sealing. Such lapping operations however, are labor intensive and increase the manufacturing costs of the valve assemblies. In addition, metal-lapped surfaces can be attacked at high temperatures by corrosive fluids, which degrades sealing over time. Sapphire, which is a very hard material that can be made flat and smooth, is less susceptible to such degradation.
Other valves may incorporate a ceramic ball that seats in a conical stainless steel orifice. Such an arrangement, however, may not provide smooth control between 2% and 100% of full scale flow.
What is still desired is a new and improved valve assembly. The valve assembly will preferably provide improved cut-off sealing, eliminate the need for hand-crafted metal parts and allow the use of impervious non-metal material for seating surfaces, and provide stable long term control valve shut-off capability. The new and improved valve assembly will also preferably provide smooth control between 2% and 100% of full scale flow, over multiple full scale ranges.